Importance of preserved periosteum around jugular foramen neurinomas for functional outcome of lower cranial nerves: Anatomic and clinical studies

Background: Surgical removal of jugular foramen (JF) neurinomas remains controversial because of their radicality in relation to periosteal sheath structures. Objective: To clarify the particular meningeal structures of the JF with the aim of helping to eliminate surgical complications of the lower cranial nerves (LCNs). Methods: We sectioned 6 JFs and examined histological sections using Masson trichrome stain. A consecutive series of 25 patients with JF neurinomas was also analyzed, and the MIB-1 index of each excised tumor was determined. Results: In the JF, meningeal dura disappeared at the nerve entrance, forming a jugular pocket. JF neurinomas were classified into 4 types: subarachnoid (type A by the Samii classification), foraminal (type B), epidural (type C), and episubdural (type D). After an average follow-up of 9.2 years, tumors recurred in 9 cases (36%). Type A tumors did not show regrowth, unlike type B tumors, in which all recurred. Radical surgery by the modified Fisch approach did not contribute to tumor radicality in type C and D tumors, even in cases in which LCN function was sacrificed. In preserved periosteum, postoperative LCN deterioration was decreased. Bivariate correlation analysis revealed that jugular pocket extension, tumor removal, MIB-1 greater than 3%, and reoperation or gamma knife use were significant recurrence factors. Conclusion: For LCN preservation, the periosteal layer covering the cranial nerves must be left intact except in patients with a subarachnoid tumor. To prevent tumor regrowth, postoperative gamma knife treatment is recommended in tumors with an MIB-1 greater than 3%.